Various manufacturing methods are employed for creating wafer interconnections. Typical wafer bonding processes involve connecting wafers using direct bond hybridization (DBH or Direct Bond Interconnection). This involves first forming posts on two wafers by electroplating on a metal seed layer through a plating mold of patterned photoresist (PR). A layer of SiO2 is then deposited over the metal structure. The surfaces are then planarized (i.e. made planar), for example, by using a chemical-mechanical polishing (CMP) process. The planar surfaces of the wafers are then aligned and bonded together and annealed.
Certain metals with low melting points, such as Indium, have desirable attributes when used as interconnections, particularly in processes requiring a compliant interconnection metal and as a non-magnetic metal. However, typical DBH interconnection manufacturing processes tend to exceed a temperature of 225 degrees Celsius. Processes at such high temperatures tend to cause low melting point metals, such as Indium which has a melting point of roughly 157 degrees Celsius, to melt and/or deform prior to interconnection. Additionally, applying CMP on a surface which includes certain low melting point interconnections can contaminate the oxide bonding surface, rendering the surface incapable of the bond strength needed for DBH.
Additionally, typical plating techniques have uniformity challenges when filling in fine pitch arrays during the process of developing interconnections. Non-uniformity in the fine pitch arrays can lead to poor interconnectivity.